Apparatus and method for adaptive whitening in a multiple antenna system

ABSTRACT

An apparatus and method for controlling a whitening function of a whitening Maximum Ratio Combining (MRC) in a receive end of a multiple antenna system are provided. The method includes identifying if there is interference from at least one neighbor cell, if there is interference, generating a weight of the whitening MRC using a pre-whitening inverse matrix, and, if there is no interference, generating a weight of the whitening MRC using a unit matrix, thus being capable of improving a reception performance of the receive end.

PRIORITY

This application claims priority under 35 U.S.C. §119(a) to a KoreanPatent Application filed in the Korean Intellectual Property Office onFeb. 10, 2009 and assigned Serial No. 10-2009-0010464, the contents ofwhich are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a pre-whitening filter of a receive endin a multiple antenna system. More particularly, the present inventionrelates to an apparatus and method for selectively using a Minimum MeanSquare Error (MMSE) scheme or a Maximum Ratio Combining (MRC) schemedepending on the existence or absence of inter-cell interference in areceive end of a multiple antenna system.

2. Description of the Related Art

With a rapid growth of the wireless mobile communication market, thereis an increase in the demand for diversity of multimedia services in thewireless environment. Accordingly, as a large capacity of transmissiondata and a high speed of data transmission are implemented to providemultimedia services, extensive research of multiple antenna systemscapable of efficiently using limited frequency resources is beingconducted.

The multiple antenna system can increase transmission reliability anddata rate compared to a single antenna system without additionalfrequency or transmission power allocation through data transmissionusing an independent channel.

The typical receiving method used in the multiple antenna system can bean MMSE scheme and an MRC scheme. In the environment in which there isinter-cell interference, an MMSE receive end has more excellentreception performance than an MRC receive end. However, when there is nointer-cell interference, the MMSE receive end exhibits a lesserreception performance than the MRC receive end. For example, when thereis no inter-cell interference, the MMSE receive end has poor receptionperformance because off-diagonal elements do not converge to ‘0’ at thetime when the R_(nn) ⁻¹ calculation necessary for MMSE weightcalculation is performed.

Thus, a receive end of a multiple antenna system needs a method forselectively using an MMSE scheme or an MRC scheme depending on theexistence or absence of inter-cell interference to improve receptionperformance.

SUMMARY OF THE INVENTION

The present invention substantially solves at least the above problemsand/or disadvantages and provides at least the advantages below.Accordingly, one aspect of the present invention is to provide anapparatus and method for selectively using a Minimum Mean Square Error(MMSE) scheme or a Maximum Ratio Combining (MRC) scheme depending on theexistence or absence of interference in a receive end of a multipleantenna system.

Another aspect of the present invention is to provide an apparatus andmethod for controlling a whitening function of a whitening MRC dependingon the existence or absence of interference in a receive end of amultiple antenna system.

A further aspect of the present invention is to provide an apparatus andmethod for controlling a whitening function of a whitening MRC dependingon a Carrier to Interference plus Noise Ratio (CINR) in a receive end ofa multiple antenna system.

The above aspects are achieved by providing an apparatus and method foradaptive whitening in a multiple antenna system.

According to one aspect of the present invention, a method forcontrolling a whitening function of a whitening Maximum Ratio Combining(MRC) in a receive end of a multiple antenna system is provided. Themethod includes identifying if there is an influence of interferencefrom at least one neighbor cell, if there is the influence ofinterference, generating a weight of the whitening MRC using apre-whitening inverse matrix, and, if there is no influence ofinterference, generating a weight of the whitening MRC using a unitmatrix.

According to another aspect of the present invention, a method forcontrolling a whitening function of a whitening MRC in a receive end ofa multiple antenna system is provided. The method includes identifyingif there is an influence of interference from at least one neighborcell, setting an update variable for a covariance matrix of noise plusinterference in consideration the influence of interference, calculatinga covariance matrix of noise plus interference, updating the covariancematrix of noise plus interference using the update variable, calculatinga pre-whitening inverse matrix using the updated covariance matrix ofnoise plus interference, and generating a weight of the whitening MRCusing the pre-whitening inverse matrix.

According to a further aspect of the present invention, an apparatus forcontrolling a whitening function of a whitening MRC in a receive end ofa multiple antenna system is provided. The apparatus includes at leastone antenna, an interference identifier, a filter controller, and apre-whitening filter. The interference identifier identifies if there isan influence of interference from at least one neighbor cell, using asignal received through the at least one antenna. If there is aninfluence of interference, the filter controller provides apre-whitening inverse matrix to the pre-whitening filter and, if thereis no influence of interference, the filter controller provides a unitmatrix to the pre-whitening filter. The pre-whitening filter generates aweight of the whitening MRC using the pre-whitening inverse matrix orunit matrix provided from the filter controller.

According to a yet another aspect of the present invention, an apparatusfor controlling a whitening function of a whitening MRC in a receive endof a multiple antenna system is provided. The apparatus includes atleast one antenna, an interference identifier, a filter controller, anda pre-whitening filter. The interference identifier identifies if thereis an influence of interference from at least one neighbor cell using asignal received through the at least one antenna. The filter controllerupdates a covariance matrix of noise plus interference using an updatevariable for a covariance matrix of noise plus interference that is setconsidering an influence of interference, and transmits a pre-whiteninginverse matrix, which is calculated using the updated covariance matrix,to the pre-whitening filter. The pre-whitening filter generates a weightof the whitening MRC using the pre-whitening inverse matrix providedfrom the filter controller.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become more apparent from the following detaileddescription when taken in conjunction with the accompanying drawings inwhich:

FIG. 1 is a block diagram illustrating whitening Maximum Ratio Combining(MRC) according to the present invention;

FIG. 2 is a block diagram illustrating a receive end in a multipleantenna system according to the present invention;

FIG. 3 is a flow diagram illustrating controlling a whitening functiondepending on an interference amount in a receive end according to anembodiment of the present invention;

FIG. 4 is a flow diagram illustrating controlling a whitening functiondepending on an interference amount in a receive end according toanother embodiment of the present invention;

FIG. 5 is a flow diagram illustrating controlling a whitening functiondepending on a Carrier to Interference plus Noise Ratio (CINR) in areceive end according to an embodiment of the present invention; and

FIG. 6 is a flow diagram illustrating controlling a whitening functiondepending on a CINR in a receive end according to another embodiment ofthe present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE PRESENT INVENTION

The following description with reference to the accompanying drawings isprovided to assist in a comprehensive understanding of exemplaryembodiments of the invention as defined by the claims and theirequivalents. It includes various specific details to assist in thatunderstanding but these are to be regarded as merely exemplary.Accordingly, those of ordinary skill in the art will recognize thatvarious changes and modifications of the embodiments described hereincan be made without departing from the scope and spirit of theinvention. Also, descriptions of well-known functions and constructionsare omitted for clarity and conciseness.

The terms and words used in the following description and claims are notlimited to their dictionary meanings, but are merely used to enable aclear and consistent understanding of the invention. Accordingly, itshould be apparent to those skilled in the art that the followingdescription of embodiments of the present invention are provided forillustration purpose only and not for the purpose of limiting theinvention as defined by the appended claims and their equivalents.

A technology for selectively using a Minimum Mean Square Error (MMSE)scheme or a Maximum Ratio Combining (MRC) scheme depending on theexistence or absence of inter-cell interference in a receive end of amultiple antenna system is described below.

In the following description, it is assumed that the receive endincludes N_(R) antennas. Here, the ‘N_(R)’ represents an integer of ‘1’or more.

Also, in the following description, it is assumed that the multipleantenna system uses an Orthogonal Frequency Division Multiplexing (OFDM)scheme. However, the present invention is applicable even when themultiple antenna system uses other communication schemes.

When there is inter-cell interference, the receive end receives a signalthat can be represented as in Equation (1). Here, Equation (1)represents a receive signal converted into a frequency domain signalthrough Fast Fourier Transform (FFT).Y=HX+H _(I) I+N  (1)

In Equation (1), ‘Y’ represents a signal received at a receive end, ‘H’represents a channel between a transmit end and the receive end, ‘X’represents a signal transmitted at the transmit end, ‘H_(I)’ representsan interference channel between a different transmit end having theinfluence of interference and the receive end, ‘I’ represents a neighborcell interference signal, and ‘N’ represents a thermal noise.

When the receive end uses an MMSE scheme, the receive end generates anMMSE weight based on Equation (2).W=E[xy ^(H) ]E[yy ^(H)]⁻¹ =H ^(H) R ⁻¹ _(yy) =H ^(H) R ⁻¹ _(nn)  (2)

In Equation (2), ‘W’ represents an MMSE weight, ‘y’ represents a receivesignal, ‘H’ represents a channel between a transmit end and a receiveend, and ‘R_(nn)’ represents a covariance matrix of noise plusinterference, ‘x’ represents a signal transmitted at the transmit end,‘R_(yy)’ represents a covariance matrix of the receive signal, ‘E[ ]’represents average of [ ]. Here, ‘H^(H)R⁻¹ _(yy)=H^(H)R⁻¹ _(nn)’ can beproved by applying a matrix inversion theorem.

The covariance matrix (R_(nn)) of Equation (2) can be given usingCholesky Factorization as in Equation (3).R _(nn) =E[nn]=LL ^(H)  (3)

In Equation (3), ‘R_(nn)’ represents a covariance matrix of noise plusinterference, ‘n’ represents the sum of noise and interference, and ‘L’represents a pre-whitening inverse matrix, ‘E[ ]’ represents average of[ ].

By applying Equation (3) to Equation (2), the MMSE weight can beexpressed in Equation (4).W=H ^(H) R ⁻¹ _(nn) _(H) =H ^(H)(LL ^(H))⁻¹=(L ⁻¹ H)^(H)(L)⁻¹  (4)

In Equation (4), ‘W’ represents an MMSE weight, ‘H’ represents a channelbetween a transmit end and a receive end, ‘R_(nn)’ represents acovariance matrix of noise plus interference, and ‘L’ represents apre-whitening inverse matrix.

When the receive end uses an MRC scheme, the receive end generates anMRC weight given in Equation (5).W _(MRC) =H ^(H)  (5)

In Equation (5), ‘W_(MRC)’ represents an MRC weight, and ‘H’ representsa channel between a transmit end and a receive end.

In a comparison between Equations (4) and (5), the MMSE weight and MRCweight have a difference of application/non-application of apre-whitening inverse matrix (L). Accordingly, as illustrated in FIG. 1the receive end can selectively use an MMSE scheme or an MRC scheme bycontrolling the pre-whitening inverse matrix (L) of a whitening MRCdepending on the existence or absence of interference. Here, thewhitening MRC represents a reception scheme designed to exhibit thereception performance of the MMSE scheme using an MRC.

FIG. 1 is a block diagram illustrating whitening MRC according to thepresent invention.

As illustrated in FIG. 1, the whitening MRC multiplies a weight by apre-whitening inverse matrix (L) to receive the same signal as that ofan MMSE scheme. At this time, a receive end selectively provides thepre-whitening inverse matrix (L) depending on the existence or absenceof interference and turns ON/OFF a whitening function of the whiteningMRC. For example, when there is inter-cell interference, the receive endprovides the pre-whitening inverse matrix (L). Accordingly, the receiveend can generate an MMSE weight given in Equation (4) and receive thesame signal as that of the MMSE scheme. As another example, when thereis no inter-cell interference, the receive end provides a unit matrix(k·I), not the pre-whitening inverse matrix (L). Accordingly, thereceive end can generate an MRC weight given in Equation (5) and receivethe same signal as that of an MRC scheme.

The following description is that of a receive end for selectivelyproviding a pre-whitening inverse matrix depending on the existence orabsence of interference.

FIG. 2 is a block diagram illustrating a receive end in a multipleantenna system according to the present invention.

As illustrated in FIG. 2, the receive end includes a plurality of RadioFrequency (RF) receivers 201-1 to 201-N_(R), a plurality of Analog toDigital Converters (ADCs) 203-1 to 203-N_(R), a plurality of OFDMdemodulators 205-1 to 205-N_(R), a plurality of interference measurementunits 207-1 to 207-N_(R), a plurality of filter controllers 209-1 to209-N_(R), a pre-whitening filter 211, and a Multiple Input MultipleOutput (MIMO) detector 213.

The RF receivers 201-1 to 201-N_(R) convert signals received throughantennas (N_(I) to N_(R)) into baseband signals.

The ADCs 203-1 to 203-N_(R) convert analog signals provided from therespective RF receivers 201-1 to 201-N_(R) into digital signals.

The OFDM demodulators 205-1 to 205-N_(R) convert time domain signalsprovided from the respective ADCs 203-1 to 203-N_(R) into frequencydomain signals through a Fast Fourier Transform (FFT) operation.

The interference measurement units 207-1 to 207-N_(R) measureinterference power in signals provided from the respective OFDMdemodulators 205-1 to 205-N_(R). For example, the interferencemeasurement units 207-1 to 207-N_(R) measure power of a combination ofnoise and interference using pilot signals. The interference measurementunits 207-1 to 207-N_(R) measure power of unused tones. If theinterference measurement units 207-1 to 207-N_(R) recognize the sum ofthe power of the unused tones as thermal noise, the interferencemeasurement units 207-1 to 207-N_(R) remove the thermal noise from thepower of combination of noise and interference and measure interferencepower.

As another example, when measuring covariance matrices (R_(nn)) of noiseplus interference in a burst, the interference measurement units 207-1to 207-N_(R) can also measure interference power in the burst.

As a further example, in the case of an Adaptive Modulation and Coding(AMC) sub-channel structure, the interference measurement units 207-1 to207-N_(R) can also measure interference power in a band.

The filter controllers 209-1 to 209-N_(R) determine if there isinterference depending on interference power provided from therespective interference measurement units 207-1 to 207-N_(R), and selectpre-whitening inverse matrices (L). For example, when there isinterference, the filter controllers 209-1 to 209-N_(R) select andprovide pre-whitening inverse matrices (L) to the pre-whitening filter211. As another example, when there is no interference, the filtercontrollers 209-1 to 209-N_(R) select and provide unit matrices (k·I) tothe pre-whitening filter 211.

The pre-whitening filter 211 filters out interference from receivesignals provided from the OFDM demodulators 205-1 to 205-N_(R). Thepre-whitening filter 211 is included in a whitening MRC. Accordingly,when receiving pre-whitening inverse matrices (L) from the filtercontrollers 209-1 to 209-N_(R), the pre-whitening filter 211 generatesan MMSE weight given in Equation (4) and receives a signal in an MMSEscheme. On the other hand, when receiving unit matrices (k·I) from thefilter controllers 209-1 to 209-N_(R), the pre-whitening filter 211generates an MRC weight given in Equation (5) and receives a signal inan MRC scheme.

The MIMO detector 213 determines a transmit signal using a receivesignal from which interference is filtered out by the pre-whiteningfilter 211 and channel information.

The following description is a method for controlling a whiteningfunction depending on the existence or absence of interference that isidentified using interference power.

FIG. 3 is a flow diagram illustrating controlling a whitening functiondepending on an interference amount in a receive end according to anembodiment of the present invention.

Referring to FIG. 3, in step 301, the receive end identifies if a signalis received from a transmit end.

If the signal is received from the transmit end, in step 303, thereceive end measures power of interference included in the receivesignal. For example, the receive end measures power of a combination ofnoise and interference using a pilot signal included in the receivesignal. Also, the receive end sums up power of unused tones andrecognizes the summed power as a thermal noise. After that, the receiveend removes thermal noise from the power of the combination of noise andinterference, and measures interference power.

After measuring the interference power, the receive end proceeds to step305 and compares the interference power measured in step 303 to athreshold interference power so as to determine if there isinterference.

If the interference power measured in step 303 is greater than thethreshold interference power, the receive end recognizes that there isinterference. Accordingly, the receive end proceeds to step 307 andselects a pre-whitening inverse matrix (L) as a whitening controlvariable. In this case, the receive end turns ON a whitening function ofa whitening MRC and receives a signal in an MMSE scheme.

On the other hand, if the interference power measured in step 303 isless than or equal to the threshold interference power, the receive endrecognizes that there is no interference. Accordingly, the receive endproceeds to step 309 and selects a unit matrix (k·I) as the whiteningcontrol variable. In this case, the receive end turns OFF the whiteningfunction of the whitening MRC and receives a signal in an MRC scheme.

After that, the receive end terminates the procedure according to theembodiment of the present invention.

In the aforementioned embodiment, a receive end selectively provides apre-whitening inverse matrix depending on the existence or absence ofinterference.

In another embodiment, a receive end can also control an update variableand turn ON/OFF a whitening function of a whitening MRC. For example,the receive end converts an ‘R_(nn)’ into an ‘LL^(H)’ form throughCholesky Factorization as given in Equation (3). Before carrying outCholesky Factorization of the ‘R_(nn)’, the receive end updates the‘R_(nn)’ as given in Equation (6).R _(nn) ^(NEW) =R _(nn) +k·I  (6)

In Equation (6), ‘R_(nn) ^(NEW)’ represents an updated R_(nn), ‘R_(nn)’represents a covariance matrix of noise plus interference, ‘k’represents an R_(nn) update variable, and ‘I’ represents a unit matrix.

As in Equation (6), the receive end updates ‘R_(nn)’ before generating apre-whitening inverse matrix (L) through Cholesky Factorization of‘R_(nn)’. At this time, the receive end can turn ON/OFF the whiteningfunction of the whitening MRC depending on ‘k’. For example, when thereis inter-cell interference, the receive end sets ‘k’ down and does notvary ‘R_(nn)’. As another example, when there is no inter-cellinterference, the receive end sets ‘k’ up. In this case, diagonalelements of ‘R_(nn)’ are relatively greater than off-diagonal elementsand thus ‘R_(nn)’ approaches a unit matrix. When the ‘R_(nn)’ is a unitmatrix, even the pre-whitening inverse matrix (L) becomes a unit matrixand thus, the whitening function can turn OFF.

Accordingly, the filter controllers 209-1 to 209-N_(R) of FIG. 2 candetermine an update variable for a covariance matrix (R_(nn)) of noiseplus interference in consideration of the influence of interference. Thefilter controllers 209-1 to 209-N_(R) calculate pre-whitening inversematrices (L) using the ‘R_(nn)’ updated using the update variable, andtransmit the calculated pre-whitening inverse matrices (L) to thepre-whitening filter 211.

The following description is made for a method for controlling an R_(nn)update variable and turning ON/OFF a whitening function of a whiteningMRC in a receive end.

FIG. 4 is a flow diagram illustrating controlling a whitening functiondepending on an interference amount in a receive end according toanother embodiment of the present invention.

Referring to FIG. 4, in step 401, the receive end identifies if a signalis received from a transmit end.

If the signal is received from the transmit end, in step 403, thereceive end measures power of interference included in the receivesignal. For example, the receive end measures power of a combination ofnoise and interference, using a pilot signal included in the receivesignal. Also, the receive end sums up power of unused tones andrecognizes the summed power as thermal noise. The receive end thenremoves the thermal noise from the power of combination of noise andinterference, and measures interference power.

After measuring the interference power, the receive end proceeds to step405 and compares the interference power measured in step 403 with athreshold interference power in order to determine if there isinterference.

If the interference power measured in step 403 is greater than thethreshold interference power, the receive end recognizes that there isinterference. Accordingly, the receive end proceeds to step 407 and setsan R_(nn) update variable (k) to a value less than a threshold value.Here, the threshold value includes a value for determining if acovariance matrix (R_(nn)) is varied through the R_(nn) update variable(k).

Then, the receive end proceeds to step 409 and calculates a covariancematrix (R_(nn)) of noise plus interference.

On the other hand, if the interference power measured in step 403 isless than or equal to the threshold interference power, the receive endrecognizes that there is no interference. Accordingly, the receive endproceeds to step 415 and sets the R_(nn) update variable (k) to a valuegreater than the threshold value.

Then, the receive end proceeds to step 409 and calculates a covariancematrix (R_(nn)) of noise plus interference.

After calculating the covariance matrix (R_(nn)) of noise plusinterference, the receive end proceeds to step 411 and updates thecovariance matrix (R_(nn)) using the R_(nn) update variable (k) set instep 407 or 415. For example, the receive end updates the ‘R_(nn)’ asgiven in Equation (6).

After updating R_(nn), the receive end proceeds to step 413 andcalculates a pre-whitening inverse matrix (L) through CholeskyFactorization of the R_(nn) updated in step 411. For example, when thereis no interference and thus the R_(nn) update variable (k) is set to avalue greater than the threshold value, the R_(nn) approaches a unitmatrix because diagonal elements of the R_(nn) are relatively greaterthan off-diagonal elements. In this case, even the pre-whitening inversematrix (L) becomes a unit matrix and thus, the receive end turns OFF awhitening function of a whitening MRC and receives a signal in an MRCscheme. As another example, when there is interference and thus theR_(nn) update variable (k) is set to a value less than the thresholdvalue, R_(nn) does not vary. Accordingly, the receive end can turn ONthe whitening function of the whitening MRC and receive a signal in anMMSE scheme.

After that, the receive end terminates the procedure according to theembodiment of the present invention.

In the aforementioned embodiment, a receive end determines if there isinterference using interference power.

In another embodiment, a receive end can also determine if there isinterference using a Carrier to Interference plus Noise Ratio (CINR).

The following description is a method for determining a pre-whiteningcontrol variable depending on the existence or absence of interferencethat is identified using a CINR.

FIG. 5 is a flow diagram illustrating controlling a whitening functiondepending on a CINR in a receive end according to an embodiment of thepresent invention.

Referring to FIG. 5, in step 501, the receive end identifies if a signalis received from a transmit end.

If the signal is received from the transmit end, in step 503, thereceive end calculates a Carrier to Interference plus Noise Ratio (CINR)for the receive signal.

After measuring the CINR, the receive end proceeds to step 505 andcompares the CINR calculated in step 503 with a threshold CINR (CINR) inorder to determine if there is interference.

If the CINR calculated in step 503 is less than or equal to thethreshold CINR (CINR_(Th)), the receive end recognizes that there isinterference. Accordingly, the receive end proceeds to step 507 andselects a pre-whitening inverse matrix (L) as a whitening controlvariable. In this case, the receive end turns ON a whitening function ofa whitening MRC and receives a signal in an MMSE scheme.

On the other hand, if the CINR calculated in step 503 is greater thanthe threshold CINR (CINR_(Th)), the receive end recognizes that there isno interference. Accordingly, the receive end proceeds to step 509 andselects a unit matrix (k·I) as the whitening control variable. In thiscase, the receive end turns OFF the whitening function of the whiteningMRC and receives a signal in an MRC scheme.

After that, the receive end terminates the procedure according to theembodiment of the present invention.

In the aforementioned embodiment, a receive end selectively provides apre-whitening inverse matrix depending on the existence or absence ofinterference.

In another embodiment, a receive end can also control an R_(nn) updatevariable and turn ON/OFF a whitening function of a whitening MRC.

FIG. 6 is a flow diagram illustrating controlling a whitening functiondepending on a CINR in a receive end of according to another embodimentof the present invention.

Referring to FIG. 6, in step 601, the receive end identifies if a signalis received from a transmit end.

If the signal is received from the transmit end, in step 603, thereceive end calculates a CINR for the receive signal.

After measuring the CINR, the receive end proceeds to step 605 andcompares the CINR calculated in step 603 with a threshold CINR(CINR_(Th)) in order to determine if there is interference.

If the CINR calculated in step 603 is less than or equal to thethreshold CINR (CINR_(Th)), the receive end recognizes that there isinterference. Accordingly, the receive end proceeds to step 607 and setsan R_(nn) update variable (k) to a value less than a threshold value.

Then, the receive end proceeds to step 609 and calculates a covariancematrix (R_(nn)) of noise plus interference.

On the other hand, if the CINR calculated in step 603 is greater thanthe threshold CINR (CINR_(Th)), the receive end recognizes that there isno interference. Accordingly, the receive end proceeds to step 615 andsets the R_(nn) update variable (k) to a value greater than thethreshold value.

Then, the receive end proceeds to step 609 and calculates a covariancematrix (R_(nn)) of noise plus interference.

After calculating the covariance matrix (R_(nn)) of noise plusinterference, the receive end proceeds to step 611 and updates thecovariance matrix (R_(nn)) using the R_(nn) update variable (k) that isset in step 607 or step 615. For example, the receive end updates theR_(nn), as given in Equation (6).

After updating the R_(nn), the receive end proceeds to step 613 andcalculates a pre-whitening inverse matrix (L) through CholeskyFactorization of the R_(nn) updated in step 611. For example, when thereis no interference and thus the R_(nn) update variable (k) is set to avalue greater than the threshold value, the R_(nn) approaches a unitmatrix because diagonal elements of the R_(nn) are relatively greaterthan off-diagonal elements. In this case, even the pre-whitening inversematrix (L) becomes a unit matrix and thus, the receive end turns OFF awhitening function of a whitening MRC and receives a signal in an MRCscheme. As another example, when there is interference and thus theR_(nn) update variable (k) is set to a value less than the thresholdvalue, the R_(nn) does not vary. Accordingly, the receive end can turnON the whitening function of the whitening MRC and receive a signal inan MMSE scheme.

After that, the receive end terminates the procedure according to theembodiment of the present invention.

The present invention has an advantage of being capable of improving areception performance of a receive end by selectively using an MMSEscheme or an MRC scheme depending on the existence or absence ofinter-cell interference in the receive end of a multiple antenna system.

While the invention has been shown and described with reference tocertain preferred embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims.

1. A method for controlling a whitening function of a whitening MaximumRatio Combining (MRC) in a receive end of a multiple antenna system, themethod comprising the steps of: identifying if there is interferencefrom at least one neighbor cell; setting an update variable for acovariance matrix of noise plus interference in consideration of theinterference; calculating a covariance matrix of noise plusinterference; updating the covariance matrix of noise plus interferenceusing the update variable; calculating a pre-whitening inverse matrixusing the updated covariance matrix of noise plus interference; andgenerating a weight of the whitening MRC using the pre-whitening inversematrix.
 2. The method of claim 1, wherein identifying if there isinterference comprises: measuring an interference power using a receivesignal; comparing the interference power with threshold interferencepower; and identifying if there is interference from the neighbor cellbased on the comparison.
 3. The method of claim 2, wherein measuring theinterference power comprises: measuring a power of a combination ofnoise and interference using a pilot included in the receive signal;measuring power of at least one unused tone; removing the power of theat least one unused tone from the power of the combination of noise andinterference; and identifying the interference power.
 4. The method ofclaim 1, wherein identifying if there is interference comprises:calculating a Carrier to Interference plus Noise Ratio (CINR) using areceive signal; comparing the CINR with a threshold CINR; andidentifying if there is interference from the neighbor cell based on thecomparison.
 5. The method of claim 1, wherein setting the updatevariable comprises: if there is interference, setting the updatevariable to a value less than a threshold value; and if there is nointerference, setting the update variable to a value greater than thethreshold value, wherein the threshold value is a value for determiningif the covariance matrix is varied through the update variable.
 6. Themethod of claim 1, wherein calculating the pre-whitening inverse matrixcomprises calculating a pre-whitening inverse matrix through CholeskyFactorization of the updated covariance matrix of noise plusinterference.
 7. An apparatus for controlling a whitening function of awhitening Maximum Ratio Combining (MRC) in a receive end of a multipleantenna system, the apparatus comprising: at least one antenna; aninterference identifier for identifying if there is interference from atleast one neighbor cell using a signal received through the at least oneantenna; a filter controller for updating a covariance matrix of noiseplus interference using an update variable for a covariance matrix ofnoise plus interference that is set considering the interference, andtransmitting a pre-whitening inverse matrix, which is calculated usingthe updated covariance matrix, to a pre-whitening filter; and thepre-whitening filter for generating a weight of the whitening MRC usingthe pre-whitening inverse matrix provided from the filter controller. 8.The apparatus of claim 7, wherein the interference identifier comparesan interference power measured using the receive signal with a thresholdinterference power, and identifies if there is interference from theneighbor cell based on the comparison.
 9. The apparatus of claim 8,wherein the interference identifier removes power of at least one unusedtone from a power of a combination of noise and interference, which ismeasured using a pilot included in the receive signal, and identifies aninterference power.
 10. The apparatus of claim 7, wherein theinterference identifier compares a Carrier to Interference plus NoiseRatio (CINR) calculated using the receive signal with a threshold CINR,and identifies if there is interference from the neighbor cell based onthe comparison.
 11. The apparatus of claim 7, wherein, if there isinterference, the filter controller sets the covariance matrix updatevariable to a value less than a threshold value and, if there is nointerference, the filter controller sets the covariance matrix updatevariable to a value greater than the threshold value, and wherein thethreshold value is a value for determining if the covariance matrix isvaried through the update variable.
 12. The apparatus of claim 7,wherein the filter controller calculates the pre-whitening inversematrix through Cholesky Factorization of the updated covariance matrix.